How to find class of bound method during class construction in Python 3.1?

When the decorator is called, it's called with a function as its argument, not a method -- therefore it will avail nothing to the decorator to examine and introspect its method as much as it wants to, because it's only a function and carries no information whatsoever about the enclosing class. I hope this solves your "riddle", although in the negative sense!

Other approaches might be tried, such as deep introspection on nested stack frames, but they're hacky, fragile, and sure not to carry over to other implementations of Python 3 such as pynie; I would therefore heartily recommend avoiding them, in favor of the class-decorator solution that you're already considering and is much cleaner and more solid.